<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>相邻兄弟选择器</title>
    <style>
        h3+p{
            color: blueviolet;
        }
    </style>
</head>
<body>
    <header>
        <h3>标题3</h3>
        <p>我是内容1</p>
        <p>我是内容2</p>
    </header>
</body>
</html>